There are several types of ophthalmologic apparatuses including ophthalmologic measuring apparatuses for measuring the properties of an eye and ophthalmologic imaging apparatuses for capturing images of an eye.
Examples of the ophthalmologic measuring apparatuses include an eye refraction test apparatus (refractometer, keratometer) for measuring the refractive properties of the eye, a tonometer, a specular microscope for obtaining the properties of the cornea (corneal thickness, cell distribution, etc.), a wavefront analyzer for obtaining the aberration information of the eye by using a Hartmann-Shack sensor, and the like.
Examples of the ophthalmologic imaging apparatus include an optical coherence tomography (OCT) apparatus for capturing a tomographic image by using OCT, a fundus camera for photographing the fundus, a scanning laser ophthalmoscope (SLO) for capturing an image of the fundus by laser scanning with the use of a confocal optical system, and the like.
In ophthalmologic examination using such an apparatus, in terms of precision and accuracy of the examination, position matching (alignment) between the optical system and the eye is important. The alignment, in general, includes the operation of matching the optical axis of the optical system with the axis of the eye (XY alignment), and the operation of matching the distance between the eye and the optical system with a predetermined working distance (Z alignment).
Japanese Unexamined Patent Application Publication No. 2013-248376 discloses a technique in which the anterior segment of the eye is photographed by two or more cameras substantially simultaneously, and alignment is performed based on the position of the characteristic site (pupil center, etc.) of the anterior segment of the eye rendered in two or more captured images. Besides, Japanese Unexamined Patent Application Publication No. 2015-85081 discloses a technique in which the anterior segment of the eye is photographed from the front while a light beam is being projected on the cornea, and alignment is performed based on a bright spot image (Purkinje image) rendered in a captured anterior eye segment image.